Method and apparatus for removing particulates

ABSTRACT

An apparatus for removing particles and/or other undesirable components from a gas stream includes a container containing a liquid, an inlet for the gas stream permitting wetting of at least a portion of the gas stream, and an outlet from the container for cleaned gas. The inlet and/or the outlet includes condensing means for cooling desired fractions of the gas stream and/or cleaned gas. The liquid may be such as to wet the particulates, thereby retaining them in the liquid while the gas passes through the liquid to the outlet. Methods for removing particulates and/or other undesirable components from a gas stream are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. national phase application of PCTInternational Application No. PCT/GB99/03930, having an internationalfiling date of Nov. 25, 1999 and claiming priority to Great BritainApplication No. 9825812.2 filed Nov. 25, 1998. The above PCTInternational Application was published in the English language and hasInternational Publication No. WO 00/30734.

This invention relates to a method and apparatus for removingparticulates and/or other undesirable components. In particular theinvention concerns such a method and apparatus for removing particulatesand/or other undesirable components from a gas stream such as an exhaustgas stream.

There are many instances when it is desirable to remove particulatesfrom a particulate-containing gas stream. For example in many industrialprocesses it is desirable for gases to be cleaned of particulates beforeundergoing eg. chemical or physical processing.

Another instance where it is desirable to remove particulates is in thefield of vacuum cleaners. Although conventional filtration techniquesare capable of removing comparatively coarse dust particles from the airflowing through a vacuum cleaner, such techniques are poor at removingfine particulates, which tend to cause various ailments, includingrespiratory disorders, if allowed to exhaust from a vacuum cleaner intothe ambient air of a room.

Another field in which particulate removal is particularly important isthat of diesel engine exhausts.

Diesel engines are widely used throughout the world, particularly inheavy vehicles (trucks, buses and trains) and increasingly inautomobiles. They are robust, fuel-efficient, long-lasting, and emitrelatively low levels of carbon monoxides but they suffer from two majordisadvantages which are causing increasing environmental concern. Theseare: (a) the emission of particulates, and (b) the emission ofundesirable components such as oxides of nitrogen, sulphur and/orpolynuclear hydrocarbons.

The particulates, which are carbonaceous in nature, are associated withundesirable hydrocarbons, of which the class known as polycyclicaromatic hydrocarbons are of particular concern. One of these compounds,3-nitrobenzanthrone, has been reported (Suzuki et al, EnvironmentScience and Technology, Volume 3, page 2772, 1997) as being extremelyactive in causing mutations in the DNA of standard strains of bacteria,as measured by the so-called Ames Test. Other compounds also present indiesel exhaust gases, such as 1,8-dinitropyrene, have also been found tobe strongly mutagenic. These observations point to a strong link betweendiesel exhaust emissions and carcinogens in the atmosphere. It has beenestimated that the tiny combustion particles, especially those withdimensions of less than 1 micrometre, are capable of carrying thesechemicals into the deep recesses of human lungs. Virtually all dieselparticles are in this size range (Michael P. Walsh “Global Trends inDiesel Emission Control—1 1997 Update”, SAE Technical Series Paper970179). Particulates from diesel exhaust gases may cause 10,000 deathsin Britain and 60,000 deaths in the USA each year. (“Dying from too muchdust”, New Scientist, Mar. 12, 1994, page 12). This leads to theconclusion of J. Merefield and I. Stone (New Scientist, Sep. 20, 1997,page 58) that “we could greatly improve our health and the urban air ifwe had better control over our vehicles' exhausts”.

Oxides of nitrogen (and ozone) are also very undesirable atmosphericpollutants because they generate oxygen radicals, which can damage DNAand attack cell membranes. Nitrogen dioxide, NO₂, emitted from dieselengines is capable of producing oxygen atoms under the influence ofsunlight, i.e.:

sunlight+NO₂→NO+O.

These oxygen atoms can then combine with oxygen in the atmosphere toform ozone, O₃, i.e.:

O+O₂→O₃.

This explains why ozone pollution is especially serious during warm,sunny days. It should be noted also that ozone is harmful not only tohumans in a number of ways (damage to airways linings, inflammatoryreactions, and increased likelihood of asthma attacks), but also tovegetation, causing reduced yields from a range of crops includingwheat, barley and peas.

Naturally, because of the worldwide concerns for these problems, therehas been a great deal of effort directed towards finding a solution. Themost obvious of these, designed to remove particulates, makes use offilters or traps. The main problem with these is that they tend tobecome blocked, which results in numerous inefficiencies in theoperation of the engines to which they are attached. This technology hasbeen studied extensively. (See, for example, Y. Teraoka et al., Catal.Today, Volume 27, page 107 (1996). It is possible to regenerate thefilters by burning off the trapped soot, and this procedure is renderedmore efficient if a catalyst is incorporated into the filter material(as referred to by J. P. A. Neeft et al. in Appl. Catal. B.Environmental, Volume 8, Page 57 (1996)). Naturally this constant needfor removal and regeneration is a serious disadvantage. An alternativeapproach has been advocated by Cooper and Thoss (SAE Technical Paper890404 (1989)). In this case a platinum-containing catalyst was mountedupstream of a particulate trap in order to oxidise nitrogen to nitrogendioxide. The resulting NO₂ is a powerful oxidising agent which iscapable of removing carbon, viz.,

2NO₂+C→2NO+CO₂.

Unfortunately, as this equation shows, the reaction generates nitricoxide. Furthermore, the catalyst is sensitive to poisoning by sulphur,which is present to a greater or lesser extent in diesel fuelsthroughout the world.

Therefore it is clear that there is a need for a system which is capableof removing particulates efficiently (especially those smaller than 1μm) and which is unaffected by the presence of sulphur.

U.S. Pat. No. 5,453,107 and U.S. Pat. No. 3,803,813 disclose apparatusfor filtering particulates from exhaust and other gases wherein the gasis first bubbled through a liquid prior to passing through a filter.

U.S. Pat. No. 5,129,926 describes an engine exhaust system comprising awater-filled scrubber tank through which the exhaust gas is released.The system further comprises a moisture trap for returning some of thecondensed gas back to the inlet manifold of the engine and a filter tofilter the gases once they have passed through the moisture trap.

U.S. Pat. No. 3,957,467 discloses an exhaust gas purifier and silencerin which exhaust gases are first released from a conduit into a liquidto purify the gas and thereafter returned to the same conduit andexhausted.

DETAILED DESCRIPTION OF THE INVENTION

According to a first aspect of the invention, there is provided a methodof removing particulates and/or other undesirable components from a gasstream, comprising wetting at least a portion of the gas stream in orderthat the particulates and/or undesirable components are entrapped and/ordissolved in the liquid thereby cleaning the gas; and further comprisingcooling the gas stream and/or cleaned gas to condense desired fractionsthereof.

This method is advantageously simple, and inexpensive since it does notrequire the expensive metals usually needed in particulate removalsystems that operate by catalysts. Also, the method of the invention hasthe capability of removing certain oxides of nitrogen and sulphur.

Desirable the majority or substantially all the gas stream is wetted.

It is to be understood that the term wetting includes both passing saidat least a portion of the gas stream through a liquid, or merely blowingthe gas stream onto the liquid in order to wet it.

Preferably the liquid is or is predominantly water, and more preferablyincludes a detergent. In preferred embodiments the detergent constitutes1 part in 50,000 of the liquid.

The detergent ensures that the liquid wets the fine particulates, andhas been found to be particularly effective when the gas stream isdiesel exhaust gas.

However, nitric oxide is only sparingly soluble in water, thus a strongoxidising agent such as ozone may be provided in order to oxidise thenitric oxide to nitrogen dioxide. The ozone may also serve to oxidiseany harmful polynuclear hydrocarbons to less harmful hydrocarbons.

Additionally, or alternatively the water may contain sodium carbonate inorder to convert any sulphur present in the gas stream to sodiumsulphate. The liquid may include antifreeze (eg. ethylene glycol). Thismakes the method of the invention more suitable for use in road vehiclesused in cold climates.

In one arrangement the step of wetting the gas stream occurs in acontainer having a splash guard for minimising fragmentation and/or lossof the liquid from the container.

This feature of the inventive method advantageously prevents the liquidfrom being thrown outwardly of the container under the force of the gasstream.

Conveniently the step of wetting the gas occurs in a vessel having anoutlet for cleaned gas, the method including the step of cooling thecleaned gas to condense desired fractions thereof. This step ensuresthat any of the liquid vaporised and conveyed to the outlet with thecleaned gas is condensed and thereby available for further use in themethod of the invention. This feature is particularly advantageous whenthe method is used to clean diesel exhaust gases, that are usually at ahigh enough temperature when passed through the liquid to vaporise thelatter. The condensing step avoids wastage of the liquid.

Typically the cooling takes place in the cleaned gas outlet. If thecleaned gas outlet is appropriately located, the condensed liquid mayflow under gravity back to the main body of liquid in the container.

The splash guard (when present) also optionally cools the cleaned gas.This may be achieved eg. by manufacturing the splash guard from amaterial having a comparatively high thermal conductivity. Many metalsare suitable.

Preferably the gas stream flows into the liquid via a submerged pipehaving a plurality of apertures defining an aggregate area at leastequal to the diameter of the pipe This feature ensures that the methoddoes not cause serious back pressure.

Alternatively the gas stream may be blown onto the surface of the liquidvia a pipe. The pipe may be positioned in the container so as to inducemixing or swirling of the liquid on blowing of the gas stream onto thesurface of the liquid. This can serve to ensure adequate wetting of thegas stream.

In turn this means that the method is useable to clean the exhausts ofinternal combustion engines, since the method can be practiced withoutsignificantly affecting the engine exhaust back pressure.

Preferably the gas stream is or includes exhaust gas from an internalcombustion engine, particularly a compression ignition engine. Themethod of the invention may also be practiced on other gas streams,including but not limited to those mentioned herein.

The method may optionally include filtering of the liquid. This mayallow a quantity of the liquid to be used several times. The inventionmay include the step of further passing a gas stream through thefiltered liquid.

According to a second aspect of the invention, there is provided anapparatus for removing particulates and/or other undesirable componentsfrom a gas stream, comprising: a container containing a liquid; an inletfor the gas stream permitting wetting of at least a portion of the gasstream; and an outlet from the container for cleaned gas wherein theinlet and/or outlet includes condensing means for cooling and condensingdesired fractions of the gas stream and/or cleaned gas. This apparatusadvantageously permits practising of the method of the invention.

Conveniently the inlet for the gas stream includes a pipe, connected toa source of the gas stream, at least partially submerged in the liquidand including one or more apertures or perforations permitting passageof the gas stream through the liquid. Preferably the aggregate surfacearea defined by the apertures in the pipe generally equals thetransverse cross-sectional area of the pipe. These features ensure thatthe apparatus of the invention does not adversely influence the pressureof the gas stream being supplied to it.

Alternatively the inlet for the gas stream includes a pipe, connected toa source of the gas stream, arranged so as to enable the gas stream tobe blown onto the surface of the liquid.

Typically the liquid is or is predominantly water, particularly waterand a detergent approximately in the ratio 1 part detergent to 50,000parts water. The liquid may also include an antifreeze. The key featuresof the liquid are that it adequately wets the particulates; and that itdoes not react undesirably with the gas. Thus any of a range of liquidsmay be suitable. For example the liquid may include an oxidising agentand/or a carbonate, such as sodium carbonate in order to assist with theremoval of undesirable components such as nitric oxide and/or sulphurfrom the gas stream. A suitable oxidising agent is ozone. Thus, in apreferred embodiment the apparatus of the invention further comprises anozone generator for providing ozone to the container. Preferably atleast a portion of the ozone is passed into the liquid.

In some instances it may not be desirable to include antifreeze in theliquid, for example to minimise cost. In such circumstances it isdesirable for the pipe to comprise further perforations which extendabove the surface of the liquid. Thus, should the liquid freeze, the gascan still escape from the pipe by way of the perforations above thefrozen liquid surface. Once the liquid defrosts, the majority of the gasstream will pass through the liquid.

These features assist in practising of the method of the invention.

Conveniently the apparatus includes a splash guard for minimisingfragmentation and/or loss of the liquid from the container. The functionof this is described above.

In preferred embodiments the splash guard includes a perforated plate,especially one having plural perforations, covering or substantiallycovering the surface of the liquid. Conveniently the splash guardincludes a wire mesh overlying the surface of the liquid. In practicalembodiments the wire mesh overlies, and covers, the perforated plate.

This design of splash guard has been found to be particularly effectivein limiting fragmentation (splashing) of a foaming liquid such as awater and detergent mix. If the splash guard (or part thereof) ismanufactured from a material, such as a metal, having good thermalconductivity, the splash guard advantageously serves to cool any liquidsplashing onto it and any gas passing through it. This tends to condenseany of the liquid vaporised by heat in the gas stream. The condensedliquid falls into the main body of liquid via the perforations, and isthus made available for re-use.

Conveniently the outlet for cleaned gas includes a pipe containing awire mesh. The wire mesh in the pipe also serves to cool and condensevaporised liquid. If the location of the pipe is correctly chosen thethus condensed liquid flows back to the main body thereof and isavailable for re-use.

Conveniently the apparatus includes a cooler for the outlet for cleanedgas. Preferably the cooler is or includes one or more cooling pipessurrounding or within the outlet and having flowing therein a coldfluid. The cooler assists in the condensation of the cleaned gas whichmay comprise vaporised liquid and thus helps to minimise evaporation ofthe liquid from the container.

The apparatus optionally includes for filtering of particulates from theliquid. Conveniently the container includes one or more apertures forfilling it with and emptying it of the liquid, thereby permitting use ofthe filter remotely of the container and return of the filtered liquidto the container. These features allow the liquid to be re-used severaltimes.

In a preferred embodiment the apparatus includes a particulate detectingdevice, operatively connected to monitoring apparatus, in the outlet forcleaned gas. This feature permits monitoring of the cleaned gas output,and if necessary can be used to indicate when filtering of the liquid isneeded.

The dependent claims hereof set out further, optional features of theinvention.

There now follows a description of preferred embodiments of theinvention, by way of example, with reference being made to theaccompanying drawings in which:

FIG. 1 is a schematic view of a first embodiment of apparatus and amethod according to the invention.

FIG. 2 is a schematic view of a second embodiment of apparatus accordingto the invention;

FIG. 3 is a schematic view of a third embodiment of apparatus accordingto the invention; and

FIG. 4 shows filtering of liquid after use of the apparatus of FIGS. 1,2 or 3.

FIG. 1 shows an apparatus 10 according to the invention comprising agenerally cylindrical container 11 having an open upper end that issealingly closed by a lid 12.

Container 11 contains a liquid 13 that is, essentially, a 1:50,000 (orother ratio) mix of a liquid detergent (ie. ARIEL FUTURE® manufacturedby Procter & Gamble and water in the embodiment shown. Other detergentsmay of course be used, in which case the ratio of detergent to water mayrequire adjustment. It is essential only that the liquid 13 is capableof wetting the fine particulates (eg. those of a diameter less than 0.1μm) described herein. The detergent/water mixture has been found to behighly successful in this regard.

Liquid 13 may also contain an antifreeze, thereby permitting use of theapparatus over a wide range of ambient temperatures, including sub-zerotemperatures.

The liquid 13 resides in approximately the lower half of container 11. Acircular plate 14, of approximately the same diameter as container 11and having formed therein a plurality of generally regularly spacedapertures 16 overlies the liquid 13.

Plate 14 may be supported by brackets or an equivalent support (notvisible in FIG. 1) that secure it within container 11.

Typically the plate 14 is formed from a metal such as stainless steel(or alloys including such metals). This confers on the plate 14 thethermal conductivity discussed herein.

Overlying plate 14 is a layer 17 of woven, knitted or otherwise mingledwire strands defining a mesh. Preferably the wire strands are ofstainless steel or aluminum containing ferritic steel; or othermaterials (including non-metals) capable of withstanding conditionswithin container 11.

An inlet pipe 18 for a particulate-containing gas stream is connected toeg. the exhaust manifold of a diesel engine, an item of process plant ora vacuum cleaner, whereby a stream of particulate-containing gas(signified by “Gas In” in FIG. 1) may be fed to the interior ofcontainer 11.

In the embodiment shown, pipe 18 optionally enlarges in diameter in twolocations, visible at 18 a and 18 b, near lid 12.

This is because the embodiment of FIG. 1 is intended for attachment tothe exhaust outlet of a diesel engine. It is important that theapparatus 10 does not induce undesirable back pressures into the exhausttract of the engine.

Pipe 18 passes downwardly, via an aperture 19, through lid 12. Pipe 18is a sealing fit in aperture 19.

From aperture 19, pipe 18 passes downwardly through a substantiallycylindrical space in layer 17 and through a further aperture 21 formedin plate 14. It is not essential for aperture 21 to seal about pipe 18.

Below plate 14 pipe 18 is reduced diameter (signified by numeral 18 c)and terminates in a curved portion located on or adjacent to the base 14a of container 11. The curvature of portion 18 c generally follows thatof the wall of container 11. Portion 18 c has formed therein anddistributed along its length a plurality of apertures 22 that allowegress of the particulate-containing gas from pipe portion 18 c into theliquid 13 in which portion 18 c is submerged.

In the embodiment shown, the pipe portion 18 c is manufactured from aflexible material although this need not necessarily be so.

On its side opposite aperture 19 lid 12 includes a further,through-going aperture 23 that is sealingly secured about a cleaned gasoutlet pipe 24. Outlet pipe 24 terminates above the surface of liquid 13so that any gas under pressure in the upper half of container 11 passesinto outlet pipe 24.

A length of pipe 24 is partially filled with a further quantity 26 ofmingled, preferably stainless steel, wire strands in a mesh. Mesh 26 mayalso be of any other material (including non-metals), in a similar wayto mesh 17. Preferably the meshes 17 and 26 are irregular.

An optional feature of the apparatus 10 is a coil or other arrangementof cooling pipes 27 that may encircle, be embedded in the walls of ormay lie within pipe 24 for the purpose of cooling the mesh 26 and anygas in pipe 24. This is achieved by circulating a coolant such as water(preferably cold water) in the pipe(s) 27, eg. by means of a per seknown coolant pump circuit of which the pipe(s) 27 form a part. Ifdesired the temperature in pipe 24 may be controlled by eg. afeedback-type control for the coolant pump.

Cleaned, cooled gas (indicated in FIG. 1 by “Cleaned gas out”) typicallyexhausts to atmosphere from the open end 24 a of pipe 24. However, ifthe apparatus 10 is used for cleaning gases for use in processequipment, pipe 24 may of course be connected to other apparatuses asnecessary.

Optionally pipe 24 may include therein, downstream of mesh 26, a device28 capable of detecting fine particulates in the gas emerging via thepipe 24. The device may be connected to an apparatus (eg. containing amicroprocessor), for monitoring the cleanliness of the gas in pipe 24.Such optional features of the invention may be used eg. to warn users ofthe need to filter the liquid 13 when it reaches its particulate-bearinglimit, or replace with fresh liquid.

The container 11 may as shown be formed partly or wholly of atransparent or translucent material such as glass or some polymericmaterials. This allows visual inspection of the condition of the liquid,which tends to darken as more and more particulates become entrained init.

FIG. 2 shows a second embodiment of the invention including severaloptional modifications. The optional modifications may be employedalone, or in combination with one another. The mesh 17 may be supportedabove the liquid in the FIG. 2 embodiment.

In the FIG. 2 embodiment the perforated portion 18 d of pipe 18 isspheroidal in shape, with the perforations spaced all around the sphere.This maximises contact of the gas with the liquid.

As shown in FIG. 2, the spheroidal portion 18 d does not have to becompletely submerged in the liquid 13. This permits a gas flow even ifthe liquid 13 freezes.

In the FIG. 2 embodiment the cooling pipes 27 optionally are dispensedwith. Instead the outlet pipe 24 may include an enlarged diameterportion 24 b containing a comparatively large amount of mesh material 26as aforesaid, that is thermally conductive. This mesh acts to condensethe exiting gas stream. This arrangement may obviate the need for acooling liquid.

Outlet pipe 24 includes a second, enlarged diameter portion 24 c thatencloses and supports a ceramic filter 28 a. The condition (ie.cleanliness) of the filter may be used to indicate any need forfiltering of the liquid 13.

Another optional feature of the invention, not visible in FIGS. 1 and 2,is for the container 11 to be substantially hemispherical. This leads tospiralling of the gas flows in the same direction in the liquid, at arate of spiralling generally proportional to engine speed.

This phenomenon gives rise to good flow characteristics in the liquid13. It also permits the generation of a large number of smaller gasbubbles in the liquid, thereby improving mixing of the gas and liquid.Also, a hemispherical chamber 11 that is approximately half full ofliquid 13 permits displacement of liquid 13, giving rise to good mixing.

FIG. 3 shows a third embodiment of the invention including furthermodifications. The optional modifications may be employed alone, or incombination with one another.

The apparatus shown in FIG. 3 further includes an ozone generator 40 assupplied for example by ozone systems, St. Helens Merseyside England.Typically such an ozone generator may generate at least 1 g/hr of ozone.Ozone generated by the generator 40 passes along pipe 42 and into theliquid 13 through a perforated end piece 44.

There now follows a description of experimental operation of theapparatus 10 (FIG. 1) when connected to the exhaust tract of a dieselengine.

Hot exhaust gas from the engine passes into the liquid 13 via pipe 18and aperture 22. Pipe portion 18 c has a large number of small apertures22, such that the total area of the apertures 22 is at least equal tothe cross-sectional area of the incoming part of pipe 18, therebyminimising back-pressure. The exhaust gas emerges through theseapertures 22 in the form of a large number of small jets, therebyensuring good interaction between the gas and the liquid 13. The splashguard comprising plate 14 and mesh 17 prevents splashing of liquid 13and causes any vapour components thereof to condense back to liquid.Mesh 26 situated in the outlet pipe 24 performs a similar function.

As previously noted the preferred liquid 13 in the container 11 iswater. However it was initially observed that if pure water is used thenparticulates begin to accumulate gradually in the outlet tube 24. Thiseffect is prevented by adding a very small concentration of detergent tothe water, ie. typically 1 part detergent in 50,000 parts of water whenthe detergent is “Ariel Futur” RTM.

When it was required for the apparatus 10 to operate efficiently also insub-zero temperatures, a liquid containing a 1:1 mixture of water andantifreeze was used. This was found to operate satisfactorily.

The efficiency of the apparatus 10 for removing particulates was testedon a single cylinder diesel engine (Lister FR1, 800 cc) mounted on atest bed and coupled to a dynamometer to enable it to be run undervarying loads. A filter 28 a (FIG. 2) in the form of a ceramic monolith(10 mm dia.×2 mm thickness) containing a multitude of channels wasmounted downstream to capture a sample of any particulates. It was foundthat in the absence of the apparatus 19 it quickly became coated withblack particulates, whereas in the presence of the apparatus 10 itremained perfectly clean. It was found also that after running theengine for several hours, by which time the liquid had become black, theliquid could be filtered through a conventional filter paper 29 (FIG. 4)remote from the apparatus 10 which collected the carbonaceous material.The liquid emerging from the filter was quite clear, and could bere-used.

Another advantage of this liquid-based system is its potential forremoving oxides of nitrogen and sulphur. Both N₂O and NO₂ are soluble inwater. NO, although only slightly soluble, can be oxidised for exampleby ozone to water-soluble NO₂. Similarly, SO₂ can be removed bydissolving in the water.

This represents an advantage over those catalytic systems which areliable to poisoning by sulphur-containing fuels.

It is understood that in the embodiments shown in FIGS. 2 and 3 portionof the gas stream does not pass into the liquid. Nevertheless, the gaspassing out of the apparatus is found to be extremely clean. Withoutwishing to be bound by any particular theory it is thought that theparticulates not passing into the liquid may be initially trapped by thewire mesh. Liquid which evaporates is in turn condensed by the coolingtubing and/or wire mesh. The condensed liquid then serves to wash thewire mesh removing the entrapped particles. Additionally oralternatively it is thought that due to the blowing action of the gasstream that a film of liquid forms on the inside surface of the spherewhich ensures wetting of the portion of the gas not passing through theliquid.

In an embodiment of the present invention where the container isgenerally cylindrical in shape and a pipe is used to blow the gas streamonto the surface of the liquid it has been advantageously found that theend of the pipe, from which the gas stream is blown, may be directedonto the surface of the liquid towards the inside wall of the container.This induces a mixing or swirling of the liquid which serves to improvethe wetting of the gas stream.

What is claimed is:
 1. A method of removing particulates and/or otherundesirable components from a an exhaust gas stream, comprising wettingby a liquid at least a portion of the exhaust gas stream by blowing theexhaust gas stream onto a surface of the liquid in a container having asplash guard for minimising loss of the liquid from the container inorder that the particulates and/or undesirable components are entrappedand/or dissolved in the liquid thereby cleaning the exhaust gas; andfurther comprising cooling the exhaust gas stream and/or cleaned exhaustgas to condense desired fractions thereof.
 2. A method according toclaim 1 wherein the liquid is or is predominantly water.
 3. A methodaccording to claim 1 wherein the liquid includes a detergent.
 4. Amethod according to claim 3 wherein the detergent constitutesapproximately 1 part in 50,000 of the liquid.
 5. A method according toclaim 1 wherein the liquid includes antifreeze.
 6. A method according toclaim 5 wherein the step of cooling takes place in an outlet for cleanedexhaust gas.
 7. A method according to claim 1 wherein the splash guardcools the cleaned exhaust gas.
 8. A method according to claim 1 whereinthe exhaust gas stream is or includes exhaust gas from an internalcombustion engine.
 9. A method according to claim 8 wherein the exhaustgas is from a compression ignition engine.
 10. A method according toclaim 1 comprising the further step of filtering the liquid to removethe particulates therefrom.
 11. A method according to claim 10 includingthe further step of further passing a gas stream through the filteredliquid.
 12. An apparatus for removing particulates and/or undesirablecomponents from a gas stream, comprising a container suitable forcontaining a liquid; an inlet for the gas stream permitting wetting ofat least a portion of the gas stream; a splash guard for minimising lossof the liquid from the container and an outlet from the container forcleaned gas wherein the inlet and/or outlet includes cooling means forcondensing desired fractions of the gas stream, and/or cleaned gas. 13.An apparatus according to claim 12 wherein the liquid is or ispredominantly water.
 14. An apparatus according to claim 12 wherein theliquid includes a detergent.
 15. An apparatus according to claim 12wherein the detergent constitutes approximately 1 part in 50,000 of theliquid.
 16. An apparatus according to claim 12 wherein the liquidincludes an antifreeze.
 17. An apparatus according to claim 12 whereinthe splash guard includes a perforated plate covering or substantiallycovering the surface of the liquid.
 18. An apparatus according to claim17 wherein the plate includes plural perforations.
 19. An apparatusaccording to claim 18 including a wire mesh overlying the surface of theliquid.
 20. An apparatus according to claim 19 wherein the wire meshoverlies the perforated plate.
 21. An apparatus according to claim 12wherein the outlet for cleaned gas includes a pipe containing a wiremesh.
 22. An apparatus according to claim 12 including a cooler for theoutlet for cleaned gas.
 23. An apparatus according to claim 22 whereinthe cooler is or includes one or more cooling pipes surrounding orwithin the outlet and having flowing therein a cold fluid.
 24. Anapparatus according to claim 22 wherein the cooler includes a mesh ofthermally conducting material in the outlet, for condensing gas in theoutlet.
 25. An apparatus according to claim 12 wherein the inlet for thegas stream includes a pipe, connected to a source of the gas stream, atleast partially submerged in the liquid and including one or moreapertures permitting passage of the gas stream through the liquid. 26.An apparatus according to claim 25 wherein the aggregate surface areadefined by the apertures in the pipe generally are equal to or greaterthan the transverse cross-sectional area of the pipe.
 27. An apparatusaccording to claim 26 wherein the area comprising the apertures isgenerally spheroidal in shape.
 28. An apparatus according to claim 12wherein the inlet for the gas stream includes a pipe arranged such thatthe gas stream is blown onto the surface of the liquid.
 29. An apparatusaccording to claim 13 including a filter for filtering of particulatesfrom the liquid.
 30. An apparatus according to claim 29 wherein thecontainer includes one or more apertures for filling it with andemptying it of the liquid, thereby permitting use of the filter remotelyof the container and return of the filtered liquid to the container. 31.An apparatus according to claim 12 including a particulate detectingdevice, operatively connected to monitoring apparatus, in the outlet forcleaned gas.
 32. An apparatus according to claim 12 including a filterin the outlet for cleaned gas.
 33. An apparatus according to claim 32wherein the filter is a ceramic filter.
 34. An apparatus according toclaim 12 wherein the container is generally hemispherical or spheroidal.35. An apparatus according to claim 12 further comprising an ozonegenerator for providing ozone to the container in order to react withundesirable components of the gas stream to reduce or substantiallyeliminate said undesirable components from being passed out of thecontainer with the cleaned gas.
 36. An apparatus according to claim 35wherein the undesirable components are selected from nitric oxide and/orpolynuclear hydrocarbons.